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LLM ComparisonGPT-5.5GPT-5.1 Codex

GPT-5.5 vs GPT-5.1 Codex

Compare GPT-5.5 and GPT-5.1 Codex. Build AI products powered by either model on Appaca.

Model Comparison

FeatureGPT-5.5GPT-5.1 Codex
ProviderOpenAIOpenAI
Model Typetexttext
Context Window1,000,000 tokens400,000 tokens
Input Cost
$5.00/ 1M tokens
$1.25/ 1M tokens
Output Cost
$30.00/ 1M tokens
$10.00/ 1M tokens

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Strengths & Best Use Cases

GPT-5.5

OpenAI

1. Strongest Agentic Coding Model

  • State-of-the-art on Terminal-Bench 2.0 (82.7%), Expert-SWE (73.1%), and SWE-Bench Pro (58.6%), outperforming GPT-5.4 on complex coding tasks.
  • Holds context across large systems, reasons through ambiguous failures, and carries changes through surrounding codebases with fewer tokens.

2. Higher Intelligence at GPT-5.4 Latency

  • Co-designed, trained, and served on NVIDIA GB200/GB300 NVL72 systems to match GPT-5.4 per-token latency while performing at a significantly higher level.
  • Uses fewer tokens to complete the same tasks, making it more efficient as well as more capable.

3. Powerful for Knowledge Work & Computer Use

  • Scores 84.9% on GDPval (44 occupations) and 78.7% on OSWorld-Verified for autonomous computer operation.
  • Excels at generating documents, spreadsheets, and reports; naturally moves across finding information, using tools, and checking output.

4. Scientific Research Co-Scientist

  • Leading performance on GeneBench, BixBench, and FrontierMath; helped discover a new proof about Ramsey numbers verified in Lean.
  • Strong enough to meaningfully accelerate progress at the frontiers of biomedical and mathematical research.

GPT-5.1 Codex

OpenAI

1. Purpose-Built for Agentic Coding

  • Designed specifically for environments where the model acts as an autonomous or semi-autonomous coding agent.
  • Optimized for multi-step reasoning in code tasks such as planning, refactoring, debugging, file generation, and tool coordination.

2. Enhanced Coding Intelligence

  • Extends GPT-5.1's advanced reasoning capabilities to handle complex software architecture decisions.
  • Better accuracy in code generation across languages (JavaScript, Python, TypeScript, Go, Rust, etc.).
  • Produces cleaner, more idiomatic code aligned with modern frameworks and best practices.

3. Superior Tool Use & Code Navigation

  • Excels at reading, understanding, and transforming multi-file codebases.
  • Works well with Codex workflows that simulate real developer tooling.
  • Strong at following function signatures, constraints, and code patterns within an existing project.

4. Long-Range Context Awareness

  • 400,000-token context window enables the model to ingest large repositories or multiple files simultaneously.
  • Supports deep analysis of project structures, dependencies, and cross-file logic.

5. Multi-Modal Development Capabilities

  • Accepts text + image input and output - suitable for tasks like:
    • Reading UI mockups or screenshots to generate code
    • Understanding architectural diagrams
    • Reviewing images of whiteboard sessions

6. Agentic Workflow Optimization

  • Built to manage longer chains of thought and execution typically required in:
    • Automated code repair
    • Project bootstrapping
    • Linting and migration tasks
    • Long-running coding agents using planning + execution loops

7. Continually Updated Model Snapshot

  • Codex-specific version receives regular upgrades behind the scenes.
  • Ensures the latest coding improvements without requiring developers to update model names.

8. Reliable Instruction Following

  • Highly consistent in honoring explicit constraints:
    • Code styles
    • Folder structures
    • API contracts
    • Framework conventions

9. Broad API Support

  • Works across Chat Completions, Responses API, Realtime, Assistants, and more.
  • Ideal for apps that need live, reasoning-heavy coding agents or generative dev environments.